Session 6 - Group work Flashcards
Most peripheral nerves, such as the median nerve are commonly referred to as “mixed spinal nerves”.
Identify 3 general characteristics of spinal nerves that give rise to use of the term “mixed spinal nerves”.
Most mammalian peripheral nerves are composed of mixtures in terms of: a) Directionality in which nerve
impulses are conducted- afferents
b) Functional Modalities represented within the nerve, sensory, motor and
autonomic
C) Myelination or lack of. Nerves are strictly divisible into two
categories; either myelinated or unmyelinated. Myleinated axons can be further teased into lightly
myelinated, or heavily myelinated
D) The speed with which nerve impulses are conducted. The speed of
nerve impulse conduction is heavily influenced by the level of myelination of the nerve in question. The
speed of conduction in myleinated axons is directly proportional to the fibre cross-sectional diameter, whilst
in unmyelinated axons it is
Name the different nerves stimulated in pain response
A alpha - Motor neurone (spinal reflex arc) A beta - Mechanoceptor A gamma - Muscle spindle) A delta and B - Sharp pain B - autonomic C - Dull, throbbing pai
When carrying out nerve conduction investigations of a specific mixed spinal nerve, which sensory
modalities would you expect to be activated at just threshold intensities of stimulation (i.e. minimal
intensities). Justify your answer.
Proprioceptors and in particular, muscle spindle afferents because these are the most heavily myelinated
nerves in the body. Since myelin reduces the capacitance of axons, it follows that the most heavily
myelinated axons would be easiest to bring to threshold by electrical stimulation since the will require
relatively less current to activate them.
6 When carrying out nerve conduction investigations of a specific mixed spinal nerve, which sensory
modalities would you expect to be activated last (i.e. maximal intensities of stimulation). Justify your answer
C-fibres (hence slow pain fibres). These are unmyelinated axons of the body. Their lack in myelin means
that their axons have a relatively high capacitance, thus, making them particularly difficult to bring to
threshold by electrical stimulation. As such, they are likely to be the last axons of the body to be activated
by electrical stimulation
History in this patient suggested that three weeks prior to the onset of pain, the affected hand became
functionally weak. She had difficulty putting her signature to documents, gripping cutlery correctly during
meals and finally her grip had weakened leading to dropping a mug full of tea. What is the explanation for
these difficulties in this patient?
The nerve is under constant compression within the carpal tunnel by the progressively growing ganglion.
This gives rise to a nerve compression syndrome. When nerves are gradually compressed, the most
myelinated axons are most susceptible to the effects of compression, presumably due to disruption of their
blood supply, leading to deprivation of nutritional substrate. In this case, the proprioceptive afferents are
thus, being selectively knocked out of action, leading to the patient being unable to carry out skilled fine
movements like putting her signature to documents. The difficulties may be arising due to lack of afferent
feedback from muscle spindle afferent axons that have succumbed to compression
8 On further questioning by the Neurologist regarding the period between prior to the onset of pain but
subsequent to motor difficulties described in Q6-7, the patient described the problematic hand as not painful
but as if “sometimes it was not mine”. What is the explanation for this lack of awareness of the hand here?
It would appear that the hand had become alien to the patient. This is likely to have arisen from
compression of proprioceptive elements of the nerves leading to a consequent lack of proprioceptive
feedback from the hand. Thus, the brain was no longer aware of proprioceptive feedback from it, hence its
alienation
One piece of the patient’s history was that just prior to the onset of severe pain, she recalled that her
hand had become numb to touch in some parts but also remembered the sensation of pins and needles.
What is the explanation for a) Numbness? B) The sensation of pins and needles.
Anaesthesia due to compression of the nerve and its attendant blood supply.
Parasthesia due to compression. The pressure on the axons of the nerve due to compression may have led
them to fire action potentials due to this non-physiological stimulus. Action potentials fired in this way would
not have been encoded correctly and as such, when they occur, the nervous system is unable to make sense
of them, hence the strange feeling of pins and needles.
History in this case indicates that when pain started to be noticeable, it seemed tolerable for a while
but gradually worsened. What is the explanation for this progression in the perception of pain in this patient?
The gradual compression of the nerve led to a gradual and progressive increase in the recruitment of pain
fibres. This would have given rise to the progressive increase in the severity of pain.
What is the explanation for the main cause of this patient’s complaint?
Nerve compression syndrome due to a space-occupying growth within the carpal tunnel
Carpal tunnel syndrome is often associated with repetitive strain injury (RSI) of the wrist. What
contribution would you expect RSI to have made to this patient’s complaint?
None in this case
What does the term “ganglion” refer to in this particular case
A tumour growing axons of a peripheral nerve
What treatment strategies might you suggest would resolve this problem a) acutely and b) long-term?
Acutely- conservatively by trying to manage the pain in the hope that the condition stabilises.
Chronically- if this case does not settle due to progression of the growth, surgical removal of the growth
may be inevitable for thre reasons: a) To relieve pain and suffering b) Reduce the possibility of this acute
pain becoming a case of chronic pain; c) Surgical removal of the growth would avail it for biopsy.
How common are soft tissue injuries as the cause of lower back pain
Most Common
6 Identify soft tissues of the back that are likely to be implicated in such a case
Muscle Tissue; Ligaments of the sacro-iliac joint; tendons of muscles
7What would be the characteristics of radiation of pain in such a case?
Local tenderness; Stiffness of back muscles: Stiffness of trunk musculature
